Rocket assisted projectile with movable piston base plate



March 25, 1969 R M. DIMOND ETAL 3,434,419

ROCKET ASSISTED PROJECTILE WITH MOVABLE PISTON BASE PLATE I Filed Aug. 10, 1967 FIG. I.

FIG. 3.

FlG. 2.

(PRIOR ART) ROBERT M. DIMOND HOWARD H. PAYNE INVENTORS.

/ 34 BY ROY ILLER 4 1 ATT NEY.

GERALD F. BAKER AGENT.

United States Patent US. Cl. 10249.3 3 Claims ABSTRACT OF THE DISCLOSURE The rocket motor of a rocket assisted projectile (RAP) is provided with a piston-type base plate to equalize the external pressure on the motor case wall during firing.

The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

Background of the invention Research directed toward extending the range of existing naval guns resulted in a rocket assisted projectile (RAP) which is realized by the incorporation of a rocket motor within the envelope of the projectile. When a RAP is fired from the gun, the rocket motor is ignited and provides additional thrust during flight. However, in any given projectile caliber, certain design criteria limit the amount of propellant which can be incorporated in the rocket motor of the projectile to provide thrust. Thus, if the amount of propellant is to be increased to attain greater range, the warhead payload or the wall thickness of the projectile might be decreased. Since the delivery of a maximum payload is, of course, most desirable, the latter solution has been sought but, as wall thickness is decreased, deflection of the case wall, because of gun gas pressure and radial engraving pressure, increases. Deflection of the case wall prevents the projectile rotating band from properly engaging the gun rifiing and causes insufficient spin to be imparted to the projectile, resulting in an unstable flight.

Summary According to this invention a piston-type base plate is provided which transfers axial forces, produced by the gun gas pressure, through the solid propellant grain to the warhead. As the propellant grain is compressed, axial forces are also translated to radial forces and these radial forces are exerted through the propellant to the inside of the case wall, offsetting the external gun gas pressures. This counteracting of the external pressures allows the use of thinner walls, thereby enabling the volume for propellant use to be increased without decreasing the payload.

Brief description of drawings FIG. 1 is a plan view of a conventional RAP; FIG. 2 is a longitudinal view in cross section of the base of the RAP according to FIG. 1; and

FIG. 3 is a longitudinal view in cross section of the base section of a RAP as modified according to the invention.

Detailed description of the invention FIG. 1 illustrates the general structure of a projectile which is designed to be fired from a weapon having a rifled bore. The projectile 10 comprises a warhead 12 and a rocket motor 14 connected at a threaded joint 11. The projectile is provided with a conventional rotating band 16. After the weapon is fired the rocket motor in the projectile is ignited by ignition means in base 24 to extend the flight of the projectile.

The casing 18 of the projectile has inserted therein the rotating band 16 which is designed to be of such material and of such dimensions that it will be engraved by the riflings of the gun barrel, thus imparting the usual stabilizing spin to the projectile. The pressure of the gun barrel on the rotating ring 16 tends to compress the projectile case and this is termed the engraving pressure.

As shown in FIG. 2, the projectile casing 18 of a conventional RAP is integral with base plate 24. Inserted in the base plate is an end plate 46 having ignition or firing means 22 therein. Heat energy supplied through ignition means 22 passes through the opening in nozzle insert 44 and through ports 38 provided in diffuser 36 to ignite the propellant 20.

When the propellant 20 has been ignited, the flow of hot gases is reversed and flows back through ports 38 and nozzle insert 44. The pressure of these gases blows out end plate 46 and the opening 40 with its tapered sides 42 then becomes the rocket nozzle.

As shown in FIG. 3, the RAP according to a practical embodiment of the present invention comprises a piston base plate 24' having a periphery of stepped configuration closely fitting into a complementary configuration in the aft end of casing 18'. The diffuser 36 has a shortened diameter, as contrasted to the diffuser 36 in FIG. 2, so that it will be free to move forward with base plate 24' without interference with heat shield 21.

Base plate 24' has a groove provided therein for an obturation seal 30 and another groove providing a seat for a spring ring 26, the purpose of which will be explained below.

Operation As the projectile is fired through the gun, gun gases apply pressure to the base plate 24' and this pressure is trans ferred through the dilfuser 36 and propellant material 20 to the Warhead 12. This arrangement accomplishes the dual purpose of (1) reducing axial forces through the motor case 18 thereby relieving the stress on the joint 11, and (2) causing axial forces to be translated by the material 20 into radial forces against the inside of the motor case 18, thus counteracting the external gun gas pressure and engraving pressure. It is evident that in the device of FIG. 3, both the base plate 24 and diffuser 36 are free to move forward. The base plate 24 is prevented from returning to its original position by means of a spring ring 26 which locks into a step 28 in the motor case when the base plate has traveled forward. An obturation seal 30 is set into a groove 32 to prevent gun gases from passing between the base plate 24' and motor case 18.

It will appear obvious to those skilled in the art that the diameter of the piston base plate may be varied to provide optimum transfer of forces under various conditions and that the spring ring 26 and seal 30 are only representative and may be pluralized or altered in shape without departing from the invention.

Conclusion said mass of propellant material and said base plate being of substantially cylindrical configuration with substantially equal cross sectional areas,

said base plate being movable to an extent necessary to transmit sufficient forces through said propellant material to counteract external gun gas pressure as Well as engraving pressure on said rotating means.

2. A projectile as defined in claim 1 wherein means is provided to limit movement of said base plate in a reverse direction.

3. A projectile according to claim 1 including:

a substantially cylindrical diffuser plate between said base plate and said propellent material,

said diffuser plate having generally flat circular end surfaces substantially commensurate and contiguous with complementary surfaces on said base plate and said mass of propellent material respectively.

References Cited UNITED STATES PATENTS 3,204,559 9/1965 De Matthew 102-49] X 3,349,708 10/1967 Paget 10249.3

FOREIGN PATENTS 373,719 4/1923 Germany.

VERLIN R. PENDEGRASS, Primary Examiner. 

